Production of disulfides



Patented Apr. 27, 1954 PRODUCTION OF DISULFIDES Willie W. Crouch'and Robert T. Workman, Bartlesville, kla., assignors to Phillips Petroleum Company, a corporation of Delaware No Drawing. Application January 2, 1951, Serial No. 204,063

Claims. 1

This invention relates to the production of bis(alkylmercaptothiocarbonyl) disulfides. In one of its specific aspects it relates to the production of bis(alkylmercaptothiocarbonyl) disulfides by oxidation of metal salts of alkyl trithiocarbonic acids. More specifically, this invention relates to the production of bis(alkylmercaptothiocarbonyl) disulfides by oxidizing a water dispersion of salts of trithiocarbonic acids using an alkali metal hypochlorite as the oxidant. In one specific embodiment our invention relates to a particularly advantageous method for producing bis(alkylmercaptothiocarbonyl) disulfides comprising controlling the pH of the reaction mixture.

The art teaches several methods for the production of compounds similar to and including bis(alkylmercaptothiocarbonyl) disulfides, all of which processes we have found to be unsatisfactory, either for the reason that the yield of desired compound is small, or undue quantities of side reaction products are obtained. 7 For instance, one method'is touse as the oxidant chlorine gas. However, when producing the bis- (alkylmercaptothiocarbonyl) disulfides of this invention we have found the'yields to be much less than desirable. V

- An object of this invention is to provide an improved method for producing 'bis(alky1mercaptothiocarbonyl) disulfides.

Another object of this invention is to provide a methodIfor the production of bis(alkylmercaptothiocarbonyl) disulfides whereby the yields of productare considerably greater than those obtained by prior art methods. u 7

Another object of this invention is to increase the ratio of bis(alkylmercaptothiocarbonyl) disulfide product to side'reaction products.

Other objects and advantages will be apparent to those skilled in the art from the accompanying discussion and disclosurej k g We have discovered an improved process for the production of increased yields of bi's(alkylmercaptothiocarbonyl) disulfides obtained by the oxidation of metal salts of alkyl trithiocarbonic acids with alkali metal hypochlorites.- Broadly, our invention comprises controlling the pH of the reaction mixture by the addition thereto of suitable quantities of acid. Additional improvement in the overall quantity of product obtained is also had by carrying out the oxidation {process using to 140 weight'per cent ofthe theoretical quantity of hypochlorit e necessary, and preferably to weight-per cent.

In accordance with our invention, which is controlling the pHof areactionj mi'xture, we have alkali .metal.

found that the most satisfactory yields, i. e., those which produce the largest quantity of bis(alkylmercaptothiocarbonyl) disulfides and smallest quantity of undesirable by-product are obtained when the pH of the solution of oxidant and material to be oxidized is maintained within the range of 4.5 to 9 and preferably within the range of 5 to 8. Such control may be obtained by the addition of the necessary quantities of an acidic material, such as acetic acid or other organic or inorganic acids, or acid salts, e. g., sodium acid sulfate, which do not otherwise affect the reaction. In this method of operation we obtain the highest yields when the alkali metal hypochlorite oxidant is used in quantities equal to the previously disclosed amounts which lie within the broad range of 100 to weight per cent of the theoretical amount required.

The temperature range preferred for all modifications of our invention are 0 to 70 F., and preferably 25 to 50" F. When operating at the lower temperatures, freezing point depressants which are not afiected under conditions of the reaction, such as acetone, may be employed if desired or necessary.

The oxidation reaction of the salts of alkyl trithiocarbcnic acids to give bis(alkylmercaptothiocarbonyl) disulfides takes place according to the following equation:

s s ZRS gSM MO 01 1110+ (RS('%S 2 2MOH MOI where R represents an alkyl radical and M is an I It is to be noted that in our process the salt of the alkyl trithiocarbonic acid reacts at the sulfuratom connected to'the alkali metaL; and not atthe alkyl group. Thus, the alkyl group does not serve as a functional group. The term alkyl is used here broadly, and is not to be"interprete d to limit applicants merely to a group which is entirely aliphatic or hydrocarbon in nature. We mean to include in addition to purely unsubstituted alkyl hydrocarbons those hydrocarbons containing ether'or thioether linkages, cycloalkyl groups, alkyl groups containing "aromatic rings substituted for hydrogen atoms -'tl1eron, or groups containing elements or radicals ter.- Alternatively, the solution may be made up 5 by reacting analkali metal hydroxide such as sodium hydroxide, carbon disulfide and an alkyl mercaptan in water according to the equation:

where R is an alkyl radical containing 1 to 12 carbon atoms.

Still another method of procedure is to prepare the salt of the alkyl trithiocarbonic acid in a non-aqueous hydrocarbon medium as described in copending application Serial No. 783,830, filed November 3, 1947, now Patent No. 2,600,737. this application a slurry of the alkali metal salt of the alkyl trithiocarbonic acid in the'supporting medium is formed. The slurry is then added in accordance with the teachings of this invention to a dilute aqueous alkali metal hypochlorite solution controlling the pH of the mixture; In this case, the aqueous solution of the alkali metal salt of the alkyl trithiocarbonic acid is produced in situ when added to the aqueoushypochlorite, i. e., the salt goes from the hydrocarbon. phase to the aqueous phase. The product of the reaction is then dissolved as it is formed in the hydrocarbon phase. We have found this mode of operation particularly suited to'continuous production when operating in this manner, that is, preparing the alkali metal salt of the alkyl trithiocarbonic acid in situ. By controlling the pH of the reaction mixture, improved results are had when operating with slow addition of one reactant to the other. Generally, we prefer to operate such that the required amount of oxidizing agent per mol of alkyl trithiocarbonic acid (100 to 140 weight per cent of thetheoretical) is added to the salt of the alkyl trithiocarbonic acid within a time limit-of to 100 minutes.

In carrying out the process of our invention, the salt of the alkyl trithiocarbonic acid preferably used is that containing 1 to 12 carbon atoms in the alkyl group and also containing an alkali metal such as sodium, potassium, or lithium. Suitable salts of alkyl trithiocarbonic acids which maybe used are exemplified by the following:

potassium tertiary octyl trithiocarbonate, sodium tertiary butyl trithiocarbonate, sodium secondary propyl trithiocarbonate, sodium primary dodecyl trithiocarbonate, and sodium cyclohexyl trithiocarbonate. The concentration of the trithiocarlccnate 1s 50 weight per cent or less of the solution pHWas controlled-to a value of about Gaby the or dispersion and is preferably in the range of 10 to 4-0 weight per cent thereof. We have obtained very satisfactory results using the trithiocarbonate in a concentration of 10 to 30 weight per cent. The alkali metal hypochlorite solution employed as oxidant can be used ina concentration in the range of 0.3 to 40 weight per cent, however, we usually prefer the range of 1 to weight per cent. In some cases both the concentration of the trithiocarbonate and the hypochlorite may vary outside these ranges, however, generally speaking, these ranges are those preferred.

W e have found that operating by the prior art method of bubbling chlorine into a .basicsolution to prepare a disulfide of the type disclosed herein is not equivalent to using an aqueous solution of an alkali metal hypochlorite, even though bubbling chlorine into an aqueous alkaline solution results in the formation of a hypochlorite. When usingchlorine as the oxidant, we have found that practically none of the desired product is ob,- tained.

Advantages of our invention are illustrated by thefollowing examples.- The reactants and their proportions and other specific ingredientsare presented as being typical and should not be construed to limit the invention unduly.

Example I In this exampl a 5.25 weight per cent aqueous solution of sodium hypochlorite was added to the sodium tertiary butyl trithiocarbonate dihydrate over a period of 30 minutes without any pH control. The yield of purified crystalline bis(tertbutylmercaptothiocarbonyl) disulfide was only 26.5 per cent of theoretical, while 11 grams of oily Joy-products were obtained.

The following example shows the beneficial effect of pH adjustment of the reaction mixture.

Example II Each of the oxidations was effected by adding a 5.25 weight per cent sodium hypochlorite solution at the rate of about 5 ml. per minute to a solution of 25 grams of sodium tertiary butyl trithioca-rbonate dissolved in200 gram-s of water. About gramsof ice Was added to keep the reaction mixture at atemperature of about 35 F. The hypochlorite was added until 15 to 20 per cent excess had been'introduced. In each case the pH of the reaction mixture was controlled at a constant pH value by. the addition of small quantities of acetic. acid.

Yield of Bis (tort-butyl- Total mercaptothiocar- Reaction bonyl) Disulfidc pH Product n ReGcovered, P t I rams ercen o G1 ams Theoretical l0 l5 13 5E) 16 l 72 12 54 3. 5 1 lo p The effect of pH adjustment of the reaction mixture is clearly shown by the results set forth in: the table. 7

Example III A 25 gram batch of sodium tertiary butyl trithiocarbonate dissolved in 100 ml. of water and 100 ml. of acetone was oxidized at 25 F. by adding 100 ml. of a 5.25 weight percent aqueous solution of sodium hypochlorite gradually While the addition of solid carbon dioxide and small amounts of acetic acid. The product precipitated in solid form as it was, produced. The solid was recovered and purified by recrystallization from acetone. A 55' per cent yield of bis(tert butyl mercaptothiocarbonyl) disulfide was obtained.

Emamplc I V Another batch of sodium tertiary butyltrithiocarbonate was prepared by reacting 22.5 grams of 9L Weight per cent pure tertiary butyl mercaptan, 11 grams sodium hydroxide, and 20 grams of carbon disulfide in 100 ml. of water. The crude reaction product was diluted with 50 ml. of water.

This was oxidized by adding 220 ml. of a 5.25 weight per cent solution of sodium hypochlorite solution slowly over a period of 30 minutes without any pH control. The yield of crystalline bis- (tert-butylmercaptothiocarbonyl) disulfide was only 26.5 per cent of theory, while 11 grams of oily lay-products was obtained.

I V Erample V Thisexam-pleis included merely to show the ef- I, III

:Eectiveness of chlorine as compared with the oxidant employed in the invention.

Chlorine gas was passed for two hours through an aqueous solution containing 30 grams of sodium tertiary floutyl trithiocarbonate. A low yield, less than 5 grams, of a mixture of a yellow solid and a lesser amount oi oil was obtained. The solid was identified as free sulfur.

As will be evident to those skilled in the art, various modifications of this invention can be followed in the light of the foregoing disclosure and discussion without departing from the spirit or scope of the disclosure or from the scope of the claims.

We claim:

1. A method for preparing bis(alkylmer'captothiocanbonyl) disulfides which comprises oxidizing an alkali metal salt of an alkyl trithiocaribonic acid with an alkali metal hypochlorite while maintaining the pH of the reaction mixture within the range of 4.5 to 9.

2. A method for preparing bis(alkylmercaptothiocarbonyl) disulfides which comprises oxidizing an alkali metal salt of an alkyl trithiocarbonic acid with an alkali metal hypochlorite at a temperature in the range of O to 70 F. while maintaining the pH of the reaction mixture Within the range of 4.5 to 9. by addition of acetic material to the reaction mixture, said salt of the alkyl trithiocarbonic acid containing 1 to 12 carbon atoms in the alkyl group. 7

3. A method for preparing bis(all;yirnercaptothiocarbonyl) disulfides which comprises oxidizing an alkali metal salt of an alkyl trithiocarbonic acid with an alkali metal hypochlorite, said salt of the alkyl trithiocarbonic acid containing 1 to 12 carbon atoms in the alkyl group, utilizing 100 to 140 weight per cent of the theoretical quantity of hypochlorite necessary to react with said salt of the alkyl trithiocarbonic acid, carrying out said oxidation ata temperature in the range of 0 to 70 F., controlling the pH of the reaction mixture within the range of 4.5 to 9 by addition of acidic material thereto, and adding the oxidizing agent to the salt of the alkyl trithiocarbonic acid within 10 to 100 minutes per mol of salt.

4. A method according to claim 3 wherein said reaction is carried out at a temperature in the range of 25 to 50 F.

5. A method according to claim 3 wherein the pH of the reaction mixture is maintained within the range of 5 to 8.

6. A method according to claim 3 wherein said salt is utilized in an aqueous solution containing not more than weight per cent of said salt.

"I. A method according to claim 3 wherein said salt of the alkyl trithiocarbonic acid is used in a non-aqueous slurry, said salt comprising not 'more than 50 weight per cent of said slurry.

8. A method according to claim 3 wherein a freezing point depressant inert tothe reaction is admixed with the reactants.

9. A method for preparing bis(alkylmercaptothiocarbonyl) disulfides which comprises oxidizing an alkali metal salt of an alkyl trithiocarbonic acid with an alkali metai hypochlorite, said salt of the alkyl trithiocarbonic containing 1 to 12 carbon atoms in the allcyl group, utilizing to weight per cent of the theoretical quantity of hypochlorite necessary to react with said salt or" the alkyl trithiocarbonic acid, utilizing said hypochlorite in a 0.3 to 49 weight per cent aqueous solution, carrying out said oxidation at a temperature in the range or 0 to 70 l t, and controlling the pH of the reaction mixture within the range of 4.5 to 9 by addition of acetic acid thereto.

10. A method according to claim 9 wherein the hypochlorite is used in a 1 to 20 weight per cent aqueous solution.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,832,163 Whitby Nov. 17, 1931 2,021,726 Hess Nov. 19, 1935 2,268,382 Cloud Dec. 30, 1941 2,270,257 Browning Jan. 20, 1942 2,453,689 Beaver Nov. 16, 1948 OTHER REFERENCES Beaver et al'., Rubber Chemistry and Technology (1944) vol. 17, pages 896--902. 

2. A METHOD FOR PREPARING BIS(ALKALYMERCAPTOTHIOCARBONYL) DISULFIDES WHICH COMPRISES OXIDIZING AN ALKALI METAL SALT OF AN ALKYL TRITHIOCARBONIC ACID WITH AN ALKALI METAL HYPOCHLORITE AT A TEMPERATURE IN THE RANGE OF 0 TO 70* F. WHILE MAINTAINING THE PH OF THE REACTION MIXTURE WITHIN THE RANGE OF 4.5 TO
 9. BY ADDITION OF ACETIC MATERIAL TO THE REACTION MIXTURE, SAID SALT OF THE ALKYL TRITHIOCARBONIC ACID CONTAINING 1 TO 12 CARBON ATOMS IN THE ALKYL GROUP. 